Talus movement in the high equatorial andes: A synthesis of ten years of data

The surficial movement of debris was monitored on a talus cone in the Venezuelan Andes for about a decade. The talus surface was classified into three textures (blocks, pebbles, sand). Painted stones were placed along four transects perpendicular to the slope; many markers (≈ 36%) were lost, mostly in pebble and sand areas, owing to burial. Mean stone movement decreased downslope, being much lower on the talus base (33.8 cm) than on the lines above (157.9, 239.9 and 107.8 cm). Tracers on blocks shifted a shorter distance (36.9 cm) than those on either pebbles (152.3 cm) or sand (225.1 cm). A regression showed that annual movement rates on 46 plots were inversely correlated with mean particle size (r=−0.878). An ANOVA indicated that the difference in rates between textures was more significant than that found between slope positions. Markers below outcrops also moved less than those on open talus. A line painted on the rockwall at the talus apex showed alternate periods of debris erosion and accretion, with an overall drop of 22.2 mm of the talus surface during a period of 11.5 years. Rates of debris movement vary substantially between talus textures because these are affected by different transport processes. Mean rates of debris movement remained essentially erratic during the study period, showing no consistent trends through time.